The variety of factors at play in environmental sound perception is
indeed puzzling and fascinating, and I wish we could investigate more
these questions.

Milena Droumeva wrote:

Further - is any difference being made in the definition of
environmental sounds between human, mechanical, electronic,
electroacoustic and digital sound?

To pursue the discussion, Milena's remark has reminded me of some
results we had in a applied study [1]. We were looking at how users
emotionally react to the manipulation of sonically interactive
interfaces. We wanted to highlight systematic relationships between
acoustical features and certain patterns in the users' reported
feelings, but it turned out that one of the main factor influencing the
valence of the reported feelings (in short, how pleasant they found the
sounds) was the "naturalness" of the sounds. This factor was
operationally defined as follows: "natural sounds" were recordings of
mechanical events consistent with the interface users were manipulating
(objects dropped on a surface), and "synthetic" sounds were created by
additive/subtractive synthesis with the specific purpose of sounding
artificial (I agree that this definition is rather tautological). Both
types of sounds shared the same low-level psychoacoustical features
(attack-time, sharpness, tonality). In another study, Patrick Susini [2]
also found that the "naturalness" (this was defined in a slightly
different way) of the sonic feedback of a mATM interface affected how
usable users perceived the interface. I have not further dug into this
question, but my feeling is that the way listeners process sounds is
different when the mechanical cause of a sound is understable (and here
I tend to believe that "understable" is strongly related to "how can I
physically make that sound"), and when no mechanical cause can be
attributed to a sound (as this is the case with certain synthetic
sounds). But the question might also not be that simple, because, to me,
a recording is like a picture: it is not a the reality, and listeners
are not fooled by it. Especially in an experiment with recordings of
natural sounds, listeners know that they are listening to recordings,
that these recordings are technical representations of something, and
"act as if" they were presented with the reality. And in the absence of
any other visual or contextual information, some recordings of naturally
occurring events can become really puzzling, a fact well known by Foley
artists. So the distinction may not be between "natural" and "synthetic"
sounds, but related to the fact that certain sounds may activate
perceptual-motor representations (say: they activate the motor
representations required to make the actions that make the sounds), and
certain may not. This might not only be related to the sounds, but also
to the listener's experience, and to contextual factors.
I wonder is someone has ever studied these questions or could point me
toward related studies.

author = {Patrick Susini and Nicolas Misdariis and Olivier Houix
and Guillaume Lemaitre },
title = {Does a ``natural" feedback affect perceived usability and
emotion in the context of use of an {ATM}?},
booktitle = {Proceedings of the Sound and Music Computing (SMC)
Conference},